Where a machine tool is used to cut work pieces, it is essential to supply cutting oil to a cutting area in order to cool heat generated at the cutting area and also reduce cutting resistance.
It is well known that a quantity of cutting oil to be supplied is controlled in response to cutting of a work piece.
For example, in Patent Document 1, cutting oil to be supplied to a cutting area is varied in quantity, depending on a change in cutting length and cutting resistance (claims 1, 2 and 3). In Patent Document 2, cutting oil to be supplied to a cutting area is controlled for a quantity thereof in response to loads of a driving motor necessary for cutting (Abstract).
A machine tool is provided with a cutting-oil tank for supplying cutting oil to a cutting area. Each of the above-described prior arts requires such a technical precondition that cutting oil is normally supplied to a cutting-oil tank as a matter of course.
However, the above-described technical precondition is not always established.
Specifically, cutting oil supplied per unit time to a cutting area is different in quantity, depending on each work piece. In the prior arts, where one or a plurality of types of work pieces are cut, a special technical consideration is not necessarily given to appropriate supply of cutting oil to a cutting-oil tank so that the cutting oil can be supplied appropriately from the cutting-oil tank on cutting each work piece.
Incidentally, Patent Document 3 has disclosed a configuration in which cutting oil separated from chips is supplied to a cutting-oil tank 3 (Abstract). However, in this case, no adjustment is made for a quantity of the cutting oil to be supplied to the cutting-oil tank after consideration is given to a quantity of the cutting oil necessary for cutting a work piece.
Patent Document 4 has disclosed a configuration in which a first cutting-oil tank and a second cutting-oil tank are adjusted so as to be substantially equal in temperature (claim 1). However, no adjustment is made for a quantity of cutting oil supplied to both the cutting-oil tanks after consideration is given to a quantity of the cutting oil necessary for cutting a work piece.
Where cutting oil is not supplied sufficiently to the cutting-oil tanks, resulting in outflow from the tanks and the cutting oil is supplied to a cutting area in a larger quantity than before, cutting work must be stopped because the cutting oil is used up in the cutting-oil tanks.
The above-described stopping inevitably causes a serious decrease in work efficiency of a machine tool.
In order to avoid the above-described state of stopping, there can be expected such a method that where cutting oil inside a cutting-oil tank reaches a minimum reference quantity, the cutting oil is automatically supplied from a cutting-oil supply source to the cutting-oil tank to realize a state in excess of the minimum reference quantity.
Cutting oil necessary for cutting work pieces is different in quantity, depending on types of work pieces. In the above-described method, a reference quantity by which the cutting oil is supplied to the cutting-oil tank is not necessarily clear, with the above difference taken into account.
As described so far, in the prior arts, it can be said that no technically significant proposal has been made about supplying cutting oil to a cutting-oil tank or a cutting area in an appropriate quantity after consideration is given to the fact that the cutting oil is different in a necessary quantity depending on the types of work pieces to be cut.